1. Field of the Invention
The present invention is related to the manufacture of semiconductor devices, and more particularly, to a method of determining the degree of charge-up induced by plasma according to a plasma process, a method for determining whether a contact hole is open using the same, a method for determining the degree of degradation of a gate insulating layer induced by plasma, and an apparatus therefor.
2. Description of the Related Art
A process of using plasma to etch a material layer is used in manufacturing semiconductor devices. For example, in a process of forming a contact hole which exposes a material layer under an insulating layer by etching the insulating layer, the insulating layer is patterned using plasma as an etching medium. At this time, charge separation may occur in an insulating layer pattern due to the electrical characteristic of the plasma. Ions accumulate inside the contact hole of the insulating layer pattern, that is, on the bottom of the contact hole due to charge separation. This so called charge-up can cause various defects in semiconductor devices. For example, when a contact hole exposing a gate electrode is formed, charge-up caused by the plasma process may degrade a gate insulating layer under the gate electrode.
For example, FIG. 1 schematically shows the distribution of charges which are charged up when a contact hole 45 is formed by a plasma process. The degradation of a gate insulating layer 20 caused by the plasma process is described in detail as follows. During formation of contact hole 45 by a plasma process, charge separation may occur at the bottom and top of the contact hole 45. That is, almost all ions of the plasma which are accelerated by a sheath travel in a straight direction, thus accumulating at the bottom of the contact hole 45 as ions 50. Meanwhile, electrons of the plasma accumulate at the upper portion of the contact hole 45 as electrons 55 due to isotropic angular momentum distribution of electrons. This means that the (−) charges are charged up in the upper portion of the contact hole 45 and the (+) charges are charged up on the bottom portion of the contact hole 45. Such a charge-up phenomenon can occur in a plasma etching process for forming a trench or a line and a space structure, as well as in a process of forming a contact hole such as contact hole 45.
Ions 50 which are accumulated at the bottom of the contact hole 45, the trench or line, or the space structure due to charge separation can have the effect that a positive voltage is applied on the gate electrode 30. This positive voltage can affect the gate insulating layer 20. Charge-up of the gate insulating layer 20 continues while the plasma process continues and charges which are charged up due to charge separation reside after the plasma process is terminated. Accordingly, the effect of applying the positive voltage to the gate insulating layer 20 is maintained. The gate insulating layer 20 may be damaged by charge-up thereof, that is, the effect of continuously applying the positive voltage may degrade gate insulating layer 20. Incidentally, when the plasma process is performed, the charge-up phenomenon caused by the plasma cannot be avoided. Also, it is not possible to prevent the material layer such as the gate insulating layer 20 from being degraded or damaged by the charge-up phenomenon.
Additionally, high integration of semiconductor devices due to a reduction in the design rule results in an increase in the aspect ratio of contact hole 45, for example. Accordingly, the line width of the bottom of the contact hole 45 is reduced and the height of the insulating layer pattern 40 is relatively increased. This makes the degree of charge-up induced by the plasma to the insulating layer pattern 40 severe. Therefore, degradation of the gate insulating layer 20 due to charge-up induced by the plasma becomes severe.
It is thus necessary to measure the degree of charge-up due to a plasma process in order to minimize or prevent damage to or degradation of the gate insulating layer caused by the plasma. A plasma damage monitoring (PDM) method has recently been used for measuring the degree of charge-up induced by the plasma. In the PDM method, the degree of damage to the gate insulating layer caused by the plasma is measured based on a change in capacitance of a wafer including the gate insulating layer. However, since the PDM method has limitations with respect to spatial resolution and calibration, the PDM method is used for measuring the degree of charge-up with respect to a flat material layer. Therefore, the PDM method has limitations in connection with measuring the degree of charge-up with respect to a wafer on which patterns are formed.